In order to characterize and quantify the substitution of Ca(II) by Cm(III) (coordination, charge compensation), homogeneous
Cm(III) coprecipitated calcite was synthesized in a mixed-flow-through experiment. Two sets of experiments were
conducted at pH 8.1 and at pH 12.5.
At pH 8.1 two calcites, a calcite with a low Cm3+ concentration (LCMpH8.1) and a calcite with a high M3+ (Gd3+ and
Cm3+) concentration (HCMpH8.1) were grown and investigated by time resolved laser fluorescence spectroscopy. The
Cm(III) emission spectra of LCMpH8.1 and HCMpH8.1 show the same Cm(III) fluorescence signals for two Cm(III) species;
Cm(III) species (1) with a peak maximum at 606.2 nm and Cm(III) species (2) with a peak maximum at 620.3 nm. Cm(III)
species (1) has a mean lifetime of s = 386 ± 40 ls and Cm(III) species (2) has a mean lifetime of s = 1874 ± 200 ls. A lifetime
of 386 ls correlates with 1.3 water molecule in the first coordination sphere of the Cm ion whereas a lifetime of 1874 ls indicates
the total loss of the Cm(III) hydration sphere. According to the fluorescence emission peak position and the fluorescence
emission lifetime, Cm(III) species (1) is identified as a surface sorbed species whereas Cm(III) species (2) is identified as a
Cm(III) incorporated into the calcite lattice.
Cm(III) fluorescence emission spectra of Cm(III) doped calcite grown at pH 12.5 (LCMpH12.5) show the same peak maxima
which are found for LCMpH8.1 and HCMpH8.1 grown at pH 8.1 but an additional emission band at 608.2 nm (3) is
found, which can be assigned to a further Cm(III) species. Fluorescence emission lifetime measurements show that this
Cm(III) species (3) has a lifetime of s = 477 ± 25 ls, which correlates with 0.9 water molecules in the first coordination sphere.
Cm(III) species (3) is suggested to be a CmOH2+ incorporated species.